1. Field of the Invention
The present invention relates to a head positioning system in a fixed magnetic disc drive, and more specifically to a head positioning system in which an amplifier is mounted on a servo head arm to amplify a servo signal that works to determine the position of the magnetic head.
2. Description of the Related Art
In a head positioning system of a magnetic recording apparatus, in general, the signal from the servo head for positioning the head and the signal from the data head for recording and play back are transmitted through signal lines of flexible circuits that are stuck onto the head arm with an adhesive agent. On a servo arm supporting the servo head is mounted an amplifier which amplifies a servo signal to reduce noise. According to the prior art for mounting the amplifier on the servo head arm as shown in FIG. 7, a flexible structure has been employed in which leads 81 of an amplifier 8 are folded in the shape of a crank to mount the amplifier. In this system, the leads 81 of the amplifier 8 are soldered onto a flexible circuit 9 that is stuck onto a servo head arm 31 to transmit servo signals. In addition, the head arm 31 of a symmetrical shape has been employed as disclosed in Japanese Patent Laid-Open Nos. 168178/1986 and 61223/1986.
A flexible structured configuration in which the leads of the amplifier are folded like a crank and the system which employs the head arm of a symmetrical shape, is adopted such that the warp of the servo head arm becomes equal to the warp of the data head arm when the environmental temperature for the magnetic recording apparatus undergoes the change. Difference in the coefficient of thermal expansion of the head arm, signal lines of the flexible circuit and of materials of the amplifier gives rise to the occurrence of a problem when the environmental temperature undergoes the change. That is, the head arm is composed of aluminum, the signal line of flexible circuit is composed of copper and the amplifier is composed of alumina ceramic. Here, aluminum has a coefficient of thermal expansion of 23.8.times.10.sup.-6 /.degree.C., copper has a coefficient of thermal expansion of 17.5.times.10.sup.-6 /.degree.C. and alumina ceramic has a coefficient of thermal expansion of 6.times.10.sup.-6 /.degree.C. When the environmental temperature is changed, therefore, the head arm develops warping due to difference in the amounts of thermal expansion of the materials. The warp of the data head arm results from a difference in the amount of thermal expansion between aluminum and copper, and the warp of the servo head arm results from a difference in the amount of thermal expansion among aluminum, copper and alumina ceramic. The coefficient of thermal expansion of the alumina ceramic is smaller than those of aluminum and copper. Therefore, the warp of the servo head arm becomes greater than that of the data head arm. Therefore, positions of the data head and the servo head are deviated from each other resulting in the development of an off-track condition of a head on the magnetic disc.
There have heretofore been employed a system of a flexible structure for mounting the amplifier by folding the leads thereof in the form of a crank and a system which uses the head arm of a symmetrical shape as mentioned above, without, however, making it possible to bring the warping amount of the data head arm into conformity with the warping amount of the servo head arm.